The present invention relates to a driving device for an auxiliary device of an engine, such as alternator, a compressor of an air conditioning device or an oil pump which is to be driven by the engine through the driving device.
These peripheral or auxiliary devices are usually driven in sole or in combination by an output power of the engine through belts 7 and 8 provided between a pulley 6 mounted on a crankshaft 5 of the engine and pulleys 3 and 4 mounted on respective input shafts 1 and 2 of the auxiliary devices, as shown in FIG. 6.
Since, among other auxiliary devices, the alternator can provide an output power which can be maintained relatively constant so long as its input shaft is rotated at a speed high enough to obtain a desired output power, it has been proposed to make the pulley 3 mounted on the input shaft of the alternator smaller than that mounted on the crankshaft of the engine to keep a rotation speed of the input shaft of the alternator high enough while making the alternator compact. When it is desired to obtain an effect which cannot obtained by making the size of the pulley 3 minimum possible size, the pulley 6 mounted on the crankshaft 5 of the engine has been made larger to increase a pulley ratio to thereby increase the rotational speed of the input shaft of the alternator.
In the latter approach, however, another problem is created. That is, in order to use another auxiliary device such as an oil pump which is to be driven by the same pulley 6 within a designed rotational speed range, the pulley 4 on the input shaft 2 thereof must be made larger with the increase of the size of the pulley 6.